Origin of Life

Question 1

List the seven shared biological characteristics of all living organisms.

Answer 1

Cellular organisation; hierarchical organisation; energy use; response to stimuli; growth; reproduction; adaptation/homeostasis

Question 2

Give the seven shared chemical characteristics of life.

Answer 2

Carbon-based; energy use; redox gradients; proteins–lipids–carbohydrates; nucleic-acid heredity; ATP as energy currency; core metabolic pathways conserved

Question 3

How old is the Universe and the Earth?

Answer 3

Universe ≈ 13.7 billion years; Earth ≈ 4.55 billion years

Question 4

What event likely formed the Moon and when?

Answer 4

Giant impact with protoplanet Thea ≈ 75 million years after Earth’s formation

Question 5

What is the Late Heavy Bombardment and its biological significance?

Answer 5

4.1–3.8 bya barrage of meteorites/comets that sterilised surface yet delivered water & organics

Question 6

Name three harsh features of the Hadean Earth.

Answer 6

5-h day length; acidic oceans with ~30 m tides & frequent boiling; anaerobic toxic atmosphere full of dust/ash

Question 7

Earliest robust evidence for life appears at what age?

Answer 7

Carbon isotope signatures ≈ 3.8 bya; stromatolite-like fossils ≈ 3.5 bya

Question 8

List six historical hypotheses for life’s origin

Answer 8

Panspermia, mineral clays, volcano/ice variants, primordial soup, acidic deep-sea vents, alkaline hydrothermal vents

Question 9

What did meteorite ALH 84001 once appear to show?

Answer 9

Possible microfossils from Mars (later judged abiotic)

Question 10

2023 Ryugu asteroid finding relevant to panspermia?

Answer 10

Detection of uracil and niacin—prebiotic organics—implying delivery of bases to Earth

Question 11

Summarise the Miller-Urey apparatus and outcome.

Answer 11

Simulated reducing atmosphere (H₂, CH₄, NH₃, H₂O) + electric sparks → amino acids via formaldehyde pathway

Question 12

Give two major criticisms of the original primordial-soup model.

Answer 12

(1) Early atmosphere likely CO₂/N₂-rich, not strongly reducing. (2) Dilution & energy issues—compounds too dispersed, lightning both creates & destroys organics

Question 13

Define the “concentration problem” in origin-of-life research.

Answer 13

Reactants must accumulate locally at high enough concentrations to react and replicate; open ocean is too dilute

Question 14

Contrast black-smoker acidic vents with alkaline vents.

Answer 14

Acidic smokers are high-temp, O₂-poor, near redox equilibrium; alkaline vents supply H₂, natural pH gradient, Fe-S catalysts, and microporous chambers to concentrate chemistry

Question 15

What geological process generates alkaline vents?

Answer 15

Serpentinisation: seawater infiltrates upper mantle, forming serpentine rock and releasing alkaline, H₂-rich fluids

Question 16

Why are proton gradients central to the alkaline-vent hypothesis?

Answer 16

Vent pH ~10–11 vs acidic early ocean pH ~5–6 → natural ΔpH could drive ATP-like chemistry before membranes evolved

Question 17

Name four features of alkaline vents that solve the concentration problem.

Answer 17

Microporous Fe-S-lined chambers; continuous flow reactors; H₂/CO₂ redox power; mineral walls as catalysts & semi-permeable barriers

Question 18

What modern field site exemplifies alkaline-vent structures?

Answer 18

The “Lost City” hydrothermal field on Atlantis Massif (discovered 2000)

Question 19

Why examine LUCA when probing life’s origins?

Answer 19

Shared biochemical traits of all extant life set a minimum feature-set and hint at the environment/chemistry where life began

Question 20

Single-sentence summary: why do alkaline vents currently lead origin-of-life models?

Answer 20

“They uniquely combine compartmentalisation, sustained H₂/CO₂ redox energy, Fe-S catalysis, and natural proton gradients—

Question 21

What is LUCA and why do we study it?

Answer 21

LUCA = Last Universal Common Ancestor; the shared biochemical toolkit of all life lets us infer the environment and chemistry present when cellular life first emerged.

Question 22

Why is LUCA unlikely to have been free-living?

Answer 22

It was probably confined within mineral ‘cells’ of alkaline hydrothermal vents, which supplied concentration, catalysts, and a proton gradient instead of a self-made membrane.

Question 23

Which biomolecule could both store information and catalyse reactions making it the best candidate before DNA and protein?

Answer 23

RNA

Question 24

Give two arguments for RNA preceding protein.

Answer 24

(1) Ribozymes show RNA can catalyse reactions; (2) an RNA strand can carry sequence information needed to specify peptides.

Question 25

Give two arguments for RNA preceding DNA.

Answer 25

(1) No universally conserved DNA-replication enzymes—bacteria and archaea use different machineries, implying DNA arose after their split; (2) DNA shows no catalytic activity, whereas RNA does.

Question 26

What discovery did Walter Gilbert (1986) highlight to support an RNA world?

Answer 26

Several RNAs (self-splicing introns, transposon RNAs) already act as enzymes, suggesting ancient catalytic roles.

Question 27

How can a two-nucleotide “code” catalyse amino-acid synthesis?

Answer 27

First base specifies precursor (e.g., C = α-ketoglutarate), second base specifies product property (e.g., U = hydrophobic AA), allowing dinucleotides to act like mini-tRNAs.

Question 28

Where do vents supply the high concentrations needed for spontaneous RNA polymerisation?

Answer 28

Microporous chambers concentrate nucleotides; convection/thermal cycling acts like PCR, promoting chain extension.

Question 29

What natural gradient in alkaline vents could power early metabolism?

Answer 29

A pH (proton) gradient: alkaline vent fluid (~pH 10) meets acidic Hadean ocean (~pH 5-6), generating ΔpH across chimney walls.

Question 30

What alternative energy carrier may have preceded ATP in vent chemistry?

Answer 30

Acetyl phosphate or other acetyl thioesters storing energy from H₂ + CO₂ redox before ATP synthase evolved.

Question 31

Why is ATP especially suited once proton gradients were harnessed?

Answer 31

ATP formation couples to proton flow (≈4 H⁺ per ATP), providing a reusable energy ‘currency’ for diverse reactions.

Question 32

What key metabolic cycle can run in reverse under vent-like conditions to build carbon compounds?

Answer 32

The reverse (reductive) tricarboxylic-acid (TCA) cycle.

Question 33

How does the Martin–Russell theory connect vents to early carbon fixation?

Answer 33

Fe-S and Ni catalysts in vent minerals enable H₂ + CO₂ → acetyl groups, feeding into reverse TCA chemistry.

Question 34

What structural innovation allowed descendants of LUCA to leave the vent?

Answer 34

Development of a self-made membrane, initially peptide-lined bubbles that later evolved into lipid bilayers.

Question 35

Why do bacterial and archaeal membranes differ fundamentally (ester- vs ether-linked lipids)?

Answer 35

Membrane evolution occurred independently after their divergence, supporting a post-LUCA origin of modern lipid types.

Question 36

Which metabolism-based lineages represent early divergences after LUCA?

Answer 36

Acetogens (acetate producers) and methanogens (methane producers), both vent-dwelling anaerobes using membrane-bound chemiosmosis.

Question 37

What evidence suggests DNA evolved from RNA not vice versa?

Answer 37

Enzymes for making deoxyribose and thymine can be derived from ribose and uracil, pointing to biochemical modification of RNA components.

Question 38

Why is DNA favourable once it appears despite RNA’s versatility?

Answer 38

Greater chemical stability and double-strand templating allow longer genomes and more accurate replication.

Question 39

Summarise the “bioreactor” concept of early life.

Answer 39

Early vent ‘cells’ acted as continuous-flow reactors where RNA, peptides, and small-molecule metabolism co-evolved before true free-living cells emerged.

Question 40

Give the lecture’s sequence of key evolutionary transitions.

Answer 40

Vent mineral cell → catalytic/self-replicating RNA → RNA-directed peptide synthesis → DNA genomes → ATP chemiosmosis → lipid membranes → free-living bacteria & archaea.

Question 41

What is the Great Oxygenation Event (GOE)?

Answer 41

A rapid rise in atmospheric O₂ between ≈2.45–2.2 billion years ago, linked to oxygenic photosynthesis and evidenced by sulfur-isotope shifts and global iron ‘rusting’.

Question 42

List three independent lines of evidence for the GOE.

Answer 42

(1) Mass-independent sulfur-isotope fractionation ends; (2) banded-iron formations/‘Great Rusting’; (3) geochemical O₂ proxies in shales/carbonates show step-increase.

Question 43

Which organisms are credited with triggering the GOE?

Answer 43

Oxygenic cyanobacteria performing water-splitting photosynthesis.

Question 44

Why is there a ≈300 Myr time lag between first cyanobacterial fossils (≈2.7 Ga) and bulk O₂ rise (≈2.45 Ga)?

Answer 44

Early O₂ was buffered by reduced volcanic gases, dissolved iron, and sulfate; significant accumulation required sinks to saturate/decline.

Question 45

State two additional geological factors (besides biology) that aided O₂ accumulation.

Answer 45

(1) Decrease in mantle melting reduced outgassing of O₂-reactive gases. (2) Tectonic compositional change lowered reductant supply to oceans/atmosphere.

Question 46

Explain how rising O₂ could trigger a global ‘Snowball Earth’.

Answer 46

O₂ oxidised CH₄ (a strong greenhouse gas) to CO₂ (weaker), reducing greenhouse warming and causing planetary glaciations (Huronian & Makganyene).

Question 47

Name two major biological consequences of the GOE.

Answer 47

(1) Extinction or retreat of anaerobes; (2) opening niches for aerobic respiration and later eukaryotic evolution.

Question 48

Why does photosynthesis provide a competitive advantage to vent-emigrant microbes?

Answer 48

It supplies both reducing power and proton gradients using abundant sunlight, replacing vent chemiosmosis.

Question 49

Define photosynthesis in metabolic terms.

Answer 49

Light-driven generation of ATP and NADPH to reduce and assimilate CO₂ into carbohydrates.

Question 50

What three resources must primitive photosynthesis supply to fix CO₂?

Answer 50

Energy (light-harvest), reducing power (electron donor/NADPH), and an enzyme catalyst (e.g., RuBisCO) with a suitable carbon-acceptor substrate.

Question 51

Describe the role of Photosystem I vs Photosystem II in bacteria.

Answer 51

PS I generates a powerful reductant for NAD(P)⁺; PS II creates a proton gradient and, in oxygenic lineages, extracts electrons from water.

Question 52

What unique cofactor enables PS II to split water?

Answer 52

The oxygen-evolving complex (OEC), a Mn₄CaO₅ cluster tethered to a tyrosine that stores and releases four oxidising equivalents.

Question 53

Why is manganese thought to pre-adapt photosynthetic water splitting?

Answer 53

Mn minerals in vents can cycle multiple valence states and absorb high-energy electrons; OEC’s (oxygen evolving complex) structure mimics vent manganese oxides.

Question 54

Outline the hypothesised sequence of photosystem evolution in prokaryotes.

Answer 54

Independent single photosystems (PS I-like or PS II-like) → gene fusion/duplication → combined two-photosystem apparatus in cyanobacteria.

Question 55

All modern photosystems share what two structural features?

Answer 55

(1) A reaction-centre core of homologous proteins; (2) bound (bacterio)chlorophyll pigments for light absorption.

Question 56

Why do different bacteria use distinct pigments?

Answer 56

Diverse pigments tune light absorption to ecological niches yet retain a common tetrapyrrole backbone, indicating shared ancestry with haem.

Question 57

Give one reason photosynthesis may have evolved on land/shallow water.

Answer 57

High UV/light exposures offer abundant energy, and surface Mn/Fe minerals could facilitate early photochemistry.

Question 58

Explain why selective loss and fusion events complicate tracing photosystem ancestry.

Answer 58

Genes encoding reaction centres can be lost, duplicated, or rearranged, producing varied present-day combinations despite shared origins.

Question 59

What is the functional payoff of combining PS I and PS II into a tandem ‘Z-scheme’?

Answer 59

Sequential light hits boost electron energy twice, enabling extraction from water and production of both ATP and strong reductant (NADPH).

Question 60

Summarise the lecture’s key take-home message in one sentence.

Answer 60

Early photosystems evolved to create independent proton gradients; their water-splitting upgrade oxygenated the planet, driving catastrophic climate shifts and paving the way for complex life.